In many industrial applications, the tightening of threaded fasteners to a specific degree or torque is of extreme importance. For example, in the assembly of automobiles or aircraft, it is imperative that nuts, bolts, screws, lugs, and the like, are tightened to a pre-specified torque to ensure the resulting assembly functions properly not only at initial use, but over the long term. Moreover, it is not sufficient that the device simply be tightened as far as possible as this may result in stripping of the threads or vibrational problems in the resulting assembly.
Accordingly, it has long been known to use torque wrenches for tightening such devices. Such wrenches are not only able to rotate and tighten the device, but also provide the user with some sort of indication as to exact torque being applied. Such devices can be as straight forward as a bendable beam type wrench having a straight strain gauge thereon, whereby the user is provided with an indication as to the torque being applied by observing the degree of deflection of the bendable beam relative to the strain gauge. The strain gauge is provided with numbered graduations to provide the user with an accurate measurement.
In still further devices, it is known to provide the torque wrench in a ratchet type of assembly wherein each rotation or click of the ratchet represents a discrete level of torque being applied. However, such a device is normally not sufficiently accurate for the specifications being set forth by the automotive and aircraft industries which commonly employ such devices. More specifically, as each click represents only a discrete number of foot pounds, any movement between clicks will result in additional torque being applied, but not measured.
In still further torque wrench designs, known as shearing stress designs, sensors are mounted to a transducer of the wrench. The sensors measure the shearing stress being applied to the transducer as the wrench is rotated. A processor is provided on the wrench to then calculate the resulting torque based on the shearing stress being measured. However, all currently known torque wrenches of such a design suffer from certain drawbacks resulting in less than optimally accurate measurements. For example, if the torque wrench is used such that force is imparted along a vector other than that causing rotation of the wrench, the transducer can tend to bend which results in shearing stress on the transducer not reflective of the torque being applied. Moreover, given the relatively uniform construction of such transducers, the shearing stress applied across the transducer is often not uniform and thus also results in inaccurate readings. Furthermore, the transducers are often mounted to a handle to which the processor is mounted using one or more pins or rivets mounted to the back of the transducer. Given such localization of the mounting structure, the transducer is subjected to bending forces making measurement of only the shearing stress resulting from the torque being applied difficult.
With the above-mentioned type of torque wrench, the transducer sensor is electrically coupled back to the processor provided on the handle. Accordingly, conductors are provided and are typically mounted on the outside surface of the transducer, thereby lending themselves to damage through normal usage. This can result in abrasion of the insulation provided about the conductor and ultimately the creation of an electrical short. This is especially true in that, although not recommended, such wrenches are often used as makeshift hammers or are otherwise mishandled. Moreover, with such torque wrenches the processor is typically provided with some sort of interface module providing the reader with a display of the torque being measured. However, given the angle at which the wrench is being used, the display is not always readily perceptible as it may be rotated or positioned at a position inconvenient for the user in taking such a measurement.